World cotton production is estimated at 24.7 million tons in 2005/06, which represents a 5.7% decline over the 2004-2005 season, while world consumption in 2006 is projected to rise to a new all-time high of 25.5 million tons, an increase of 1.7 million tons or 7.4% from last season. The use of cotton, wool, and silk increased 7.0% to 26.8 million tons in 2005, a growth rate over four times than that of man made fiber use. From these figures, it should be apparent that cotton consumption is exceeding production. Moreover, the equilibrium price of stock has increased as seen in the Cotlook A Index (from about $0.50/lb at the beginning of the 2005 to $0.60 in the fourth quarter of 2005). The United States produced 23.9 million bales of mostly American Upland Cotton in 2005 at an average price per pound of $0.56. At 480 pounds per bale, the U.S. cotton industry represents a $6.4 billion market. The International Fiber Journal also forecasts world cotton area for 2005/06 at 34.7 million hectares, down 3.1% from 2004/05. Additionally, cotton yields declined from 732 kg/hectare in 2004/05 to 712 kg/hectare in the current season. Changes in the cultivated area and yield pose reliable planning issues for the downstream spinning industry and a threatened means of existence to farmers.
The average cotton farmer targets cotton fiber length to be produced at 34/32 inches. If the average cotton fiber length is 33/32 inches or less the fiber doesn't command the premium of its longer ( 35/32 in.) cousin. An opportunity exists for a new technology to allow farmers, by replacing only their gins, to increase yield by approximately 7% and command a premium due to long staple length of fibers that might be produced by a new gin from the same seed cotton. This increased fiber length combined with comparable or better yield will ensure the farmer competitiveness and likely increase profits.
The cotton saw gin was developed in 1794 by Eli Whitney as a way of separating the useful cotton fiber from the cotton seeds (which are not used in cotton products). Only a few improvements have been made to the cotton gin since Eli Whitney's saw gin. Prior to the development of the saw gin, the roller gin (see FIG. 4) was used and most acknowledge that it was the first mechanical device used for ginning cotton. The roller gin used two rollers similar to a latter-day clothes wringer that pinched and pulled cotton fibers from cotton seeds. This allowed production of cotton fibers on the order of about 5 pounds of lint per day. This roller gin or “churka” was the primary ginning tool until Eli Whitney patented the saw gin in 1794.
Whitney's saw gin removed seeds from the cotton fibers with a spiked cylinder that pulled the lint through wooden slots too narrow for the seeds to pass through. The saw gin was 50-100 times faster than hand ginning. It was especially effective in separating the hard to remove seeds in Upland cotton, making these short staple cottons more economical to produce than previously. Improvements were subsequently made to Whitney's saw gin such as replacing the spikes in Whitney's saw gin with circular serrated saws that have made it more effective for separating seed and fiber. The process of saw ginning is shown in FIGS. 2 and 3a-d. In FIG. 2, the raw cotton goes in a slot and the seeds drop through the slot and cotton fibers are blown out. In 3a, the saw teeth rotate to hook fibers and strip seeds. In 3b the fibers on the saw teeth are pulled through slots. 3c shows the seeds that are stripped of fiber as the fall out the slot. FIG. 3d shows a rapidly revolving brush that sweeps the fibers off the saw teeth while forced air blows fibers off the brushes out the gin. Subsequent improvements of Whitney's saw gin have allowed the production of about 15 bales of lint per hour per stand.
The saw gin was (and is) much faster than the roller gin but it did not replace the roller gin entirely. Although the roller gins cotton more slowly, it is gentler to the cotton than the saw gin. The saw gin possesses serrated saws that tend to break more of the cotton fibers. Roller gins, although slower, continue to be used for ginning Pima cotton to protect the extra-long staple or length, a desirable quality that increases the value of the cotton fiber.
The roller gin continued to be used for ginning extra-long-staple cottons, but its low ginning rate made it too expensive to maintain and operate. In an effort to increase its ginning capacity, several gins were developed that improved the roller ginning rate, though these improvements did not dramatically improve the ginning rate. It wasn't until the 1960's, when the rotary-knife gin was developed at the Southwestern Cotton Ginning Research Laboratory in cooperation with gin manufacturers and private ginneries, that roller gins became more efficient and less expensive to operate.
The rotary-knife gin improved on the McCarthy gin invented by Fones McCarthy in 1840. It retained the McCarthy Gin's ginning roller and stationary knife, but replaced its reciprocating knife with a rotary knife that greatly increased the roller ginning rate. Compared to the McCarthy Gin which produces only ¼ bale of lint an hour per stand, the rotary-knife gin can produce up to 1½ bales of lint an hour per stand. The McCarthy roller gin uses a method of positioning a stationary knife tightly against a ginning roller and a reciprocating knife blade to dislodge the seed from a pinch point. Nevertheless, even with subsequent improved methods that increased the speed of feeding the machine, the McCarthy rotary-knife gin still suffered the drawback of low capacity. The subsequent introduction of the rotabar in the 1960s allowed the production rate of the roller gin increased to a rate of about two bales per hour and the amount of lint left on the seed was reduced to a level that has been calculated to be about 6.6 percent. However, the rates attained by the rotabar are still far inferior to the 15 bales of hour that can be attained by the machine descendents of the Whitney saw gin. Despite these speed limitations, the roller gin is advantageous in that there are small amounts of short fiber with a concomitant increase in fiber strength and increased uniformity.
Each of the above mentioned gins have their advantages, but all also have drawbacks. The saw gin is faster but does not provide the longer desirable fibers. The roller gin produces the longer desirable fibers but is much slower. Accordingly, it is with the above considerations in mind the instant invention was developed.